The present invention relates to a wireless transmitter useful in mobile communication systems such as personal communications systems and digital cellular telephone systems.
Mobile digital communication systems operating by code division multiple access (CDMA), time division multiple access (TDMA), and frequency division multiple access (FDMA) are well known. There is currently much interest in using these systems for multimedia communication, as in the wideband coherent CDMA system developed in Japan. A transmitter in this CDMA system multiplexes two or more types of data with different quality requirements into a single frame, encodes each frame with an error-correcting convolutional code having a ⅓ code rate, and interleaves each coded frame as a safeguard against burst errors. A spreading modulator spreads the interleaved signal, which is then band-limited by a low-pass filter and modulated onto a radio-frequency carrier signal that is radiated from an antenna.
A problem in this system and other similar systems is that all types of transmitted data are coded with the same error-correcting code, and transmitted at the same transmitting power level. Consequently, the error rate for all types of transmitted data is the same, even though the different quality requirements of the data place different requirements on the error-rate.
If, for example, the transmitter multiplexes data having a maximum allowable error rate of 10xe2x88x923 with data having a maximum allowable error rate of 10xe2x88x926, then the transmitter must operate at a power level sufficient to satisfy the more stringent requirement (10xe2x88x926). Consequently, the data having an allowable error rate of 10xe2x88x923 are transmitted at an unnecessarily high power level.
This unnecessarily high power level generates undesired interference with other signals. In particular, in a CDMA system, in which multiple signal channels share the same radio-frequency band, interference limits the number of users who can access the system simultaneously. In TDMA and FDMA systems, interference power limits spectrum efficiency by constraining the channel reuse factor.
It is accordingly an object of the present invention to eliminate excess transmitting power when different types of data, having different quality requirements, are multiplexed and transmitted on a single wireless channel.
The invented wireless transmitter transmits at least two different types of data, with different quality requirements, on a single wireless channel. The transmitter has a multiplexer that multiplexes the different types of data into frames. Each frame includes a plurality of different types of data. A power controller controls the transmitting power of each type of data individually within each frame, according to the quality requirement of the type of data, so that each type of data is transmitted at the power necessary to obtain the required quality.
Excess transmitting power is eliminated because no type of data is transmitted with more than the necessary power.